1. Field of the Invention
The present invention relates to a body frame structure for a four-wheeled buggy.
2. Description of the Related Art
Japanese Patent Publication No. Hei 7-41861 discloses a body frame for a four-wheeled buggy. The body frame is constructed by separately preparing a front body frame for supporting an engine, and a sub-frame (rear body frame) for supporting a load-carrying platform. Upper fastening portions are provided on seat rails and back tubes of the sub-frame for obliquely connecting the seat rails to lower frames passing under the engine.
In the above structure, the upper and lower fastening portions provided on the sub-frame are fastened to the seat rails and the back tubes. Accordingly, if the body frame is constructed by welding the front body frame, such as the back tubes and the seat rails to each other, then when fastening the sub-frame to the front body frame, the dimensions of the seat rails and the back tubes to which the upper and lower fastening portions are to be fastened, may deviate due to the welding of the back tubes to the seat rails. This makes it difficult to maintain dimensional accuracy of the portions of the seat rails and the back tubes to which the upper and lower fastening portions are to be mounted and hence to readily assemble the sub-frame to the front body frame.
To solve such a difficulty in constructing the body frame by fastening the sub-frame to the already assembled front body frame, the body frame must be constructed by fastening the seat rails and the back tubes to the sub-frame before welding the back tubes to the seat rails. The front body frame is then constructed by welding components such as the back tubes and the seat rails to each other.
However, in the above-described assembling process, since the large-sized members, which are substantially comparable to the body frame, must be assembled by welding, the handling performance is degraded and the assembling efficiency is significantly reduced. Accordingly, it is desirable to separately sub-assemble the front body frame and the rear body frame and then fasten the sub-assemblies to each other in order to construct the body frame.
Further, the body frame is required to have a high rigidity against a transverse load applied to the seat rails. That is, high transverse rigidity is required when the body frame is used with a four-wheeled buggy of the type including two front wheels and two rear wheels, wherein the rear wheels are supported via a common axle on the right and left sides of a rear end of a rear swing arm with its front end swingably supported to a vehicular body. To be more specific, for such a four-wheeled buggy of this type, a torsional force is applied to a vehicular body when the buggy is turned, and even during usual running with no turning, a torsional force is also applied to the vehicular body due to a difference in height between the two rear wheels when the buggy runs on irregular road surfaces. As a result, the vehicular body of the four-wheeled buggy of this type, particularly, a sport buggy is required to have a transverse rigidity much larger than that of a saddle type motorcycle.
To solve the above-described problems, according to the present invention, there is provided a body frame structure for a four-wheeled buggy of a type which includes two front wheels and two rear wheels, the rear wheels being supported via a common axle on right and left sides of a rear end of a rear swing arm with its front end swingably supported by a vehicular body, the body frame structure including: a front body frame for supporting an engine, and a rear body frame for supporting a seat, the front body frame and the rear body frame being previously constructed into different sub-assemblies and then fastened to each other into one-body; wherein the front body frame includes a pair of right and left main frames extending in the longitudinal direction while passing above the engine, and a pair of right and left center frames extending downwardly from rear ends of the main frames while passing behind the engine, and the rear body frame includes a pair of right and left seat rails for supporting a saddle type seat, a pair of right and left upper fastening portions provided at front ends of the seat rails, and a pair of right and left lower fastening portions provided under the upper fastening portions; and wherein the right and left upper fastening portions are connected to each other with a cross member, and the right upper fastening portion and the right lower fastening portion are commonly fastened to the right center frame and the left upper fastening portion and the left lower fastening portion are commonly fastened to the left center frame.
With this configuration, since the portions, to which the upper and lower fastening portions of the rear body frame are to be mounted, are formed on the same members, that is, the center frames, the upper and lower fastening portions of the rear body frame can be fastened to the same members, as opposed to different members as is conventionally known. Accordingly, even if the main frames are welded to the center frames to sub-assemble the front body frame before the rear body frame is fastened to the front body frame, it is possible to keep dimensional accuracy between the portions to which the upper and lower fastening portions are to be fastened, without being adversely affected by the welding process.
As a result, the work of constructing the body frame can be facilitated by separately sub-assembling the front body frame and the rear body frame, and constructing the body frame by integrally fastening the sub-assemblies to each other.
Also, since the upper fastening portions provided at the right and left front ends of the seat rails are connected to each other with the cross member, it is possible to ensure the strength of the upper fastening portions, and hence to increase the transverse rigidity of the body frame. Accordingly, the body frame having such a high transverse rigidity can be suitably used for a four-wheeled buggy of a type including two front wheels and two rear wheels, wherein the rear wheels are supported via a common axle on the right and left sides of a rear end of a rear swing arm with its front end swingably supported by a vehicular body. The body frame is also applicable to a sport buggy which particularly requires a high transverse rigidity.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.